Dental treatments comprising implanting a dental implant at a site where a tooth or teeth are missing, and, with the dental implant as a root, attaching an artificial tooth onto the top of the dental implant as a substitute for a natural tooth, have been clinically applied, and are known in the art.
Such dental implants are conventionally made of metals such as titanium and a cobalt/chromium/molybdenum alloy. In recent years, alumina ceramics have received increasing attention because of the superior in vivo characteristics thereof, and are now in widespread use.
Various techniques for implanting a dental implant are known; a very popular technique is as follows:
Mucosa at a site where a tooth or teeth are missing is peeled apart, a grooved or tapped hole conforming to the shape of the root portion of the dental implant is formed in a jaw bone, and thereafter, the dental implant is placed in the hole and the mucosa is closed. In accordance with another method, a dental implant is implanted in a tooth extraction hole.
These methods, however, suffer from the following disadvantages:
(1) Although metal has sufficiently high mechanical strength, it has poor affinity for human bones because of their different properties. Moreover, the metal can be ionized and eluded, exerting adverse influences on the human body.
(2) Although alumina ceramics are not harmful to human body, they are very hard compared with human bones and have poor affinity therewith. Therefore, when a dental implant of such alumina ceramics is used for a long period of time, a clearance is formed, resulting in damage to the jaw bone at the adhesion site.
It is described in Japanese patent application (OPI) No. 50194/79 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") that the surface of stainless steel can be coated with calcium phosphate to alleviate the foregoing problems. However, this calcium phosphate is gradually replaced in vivo by bone tissue and, finally, the bone and stainless steel may come into contact with each other.
There is also a danger of stainless steel's corroding over a long time period of use, and exerting adverse influences on the human body.